Presence Of Ethylenediaminetetraacetic Acid Research Articles

Domain coupling in a multimodular cellobiohydrolase CbhA from Clostridium thermocellum

Cellobiohydrolase A (CbhA) from Clostridium thermocellum is composed of an N-terminal carbohydrate-binding domain 4 (CBD4), an immunoglobulin-like domain (Ig), a glycoside hydrolase 9 (GH9), X11 and X12 domains, a CBD3, and a dockerin domain. All domains, except the Ig, bind Ca2+. The following constructs were made: X12, X11X12, CBD3, X11X12-CBD3, Ig, GH9, Ig-GH9, Ig-GH9-X11X12, and Ig-GH9-X11X12-CBD3. Interactions between domains in (1) buffer, (2) with Ca2+, or (3) ethylenediaminetetraacetic acid (EDTA) were studied by differential scanning calorimetry. Thermal unfoldings of all constructs were irreversible. Calcium increased Td and cooperativity of unfolding. Multi-domain constructs exhibited more cooperative unfolding in buffer and in the presence of EDTA than did individual domains. They denatured by mechanism simpler than expected from their modular architecture. The results indicate that domain coupling in thermophilic proteins constitutes a significant stabilizing factor.

Selective separation of yttrium by CA-100 in the presence of a complexing agent

The selective separation of Y from yttrium solution containing small heavy rare earth (HRE) impurities (Ho, Er, Tm, Yb, Lu) by liquid–liquid extraction using CA-100 in the presence of a water-soluble complexing agent of ethylenediaminetetraacetic acid (EDTA) was experimentally studied at 298 K. Experiments were carried out in two feeds, Feed-I: [RE] f = 4.94 × 10 −3 M, Y = 98.5%, HRE (Ho, Er, Tm, Yb, Lu) = 1.5%; Feed-II: [RE] f = 4.94 × 10 −3 M, Y = 99.9%, HRE (Ho, Er, Tm, Yb, Lu) = 0.1%, as a function of equilibrium pH (pH eq), the concentration ratio of [EDTA]:[HRE impurities]. It was shown that the extraction of HRE in the presence of EDTA was suppressed when compared to that of Y because of the masking effect, while the selective extraction of Y was enhanced and the separation factors increased to maximum at appropriate condition for Feed-I: Y/Ho = 1.53, Y/Er = 3.09, Y/Tm = 5.61, Y/Yb = 12.04, Y/Lu = 27.51 at pH 4.37 and [EDTA]:[HRE impurities] = 4:1, for Feed-II: Y/Ho = 1.32, Y/Er = 1.91, Y/Tm = 2.00, Y/Yb = 3.05, Y/Lu = 3.33 at pH 4.42 and [EDTA]:[HRE impurities] = 8:1. The separation and purification of Y by this method was discussed.

Influence of heat processing and calcium ions on the ability of EDTA to inhibit lipid oxidation in oil-in-water emulsions containing omega-3 fatty acids

The nutritional benefits of ω-3 fatty acids make them excellent candidates as functional food ingredients if problems with oxidative rancidity can be overcome. Oil-in-water emulsions were prepared with 2% salmon oil, stabilized by 0.2% Brij 35 at pH 7. To determine the effects of heating (50–90 °C), ethylenediaminetetraacetic acid (EDTA), and calcium on the oxidative and physical stability of salmon oil-in-water emulsions, particle size, thiobarbituric acid reactive substances (TBARS), and lipid hydroperoxides were measured. The heat-processed emulsions showed no significant difference, in particle size, TBARS or hydroperoxides during storage, from unheated emulsions. Above 2.5 μM, EDTA dramatically decreased lipid oxidation in all samples. Addition of calcium to emulsions containing 7.5 μM EDTA significantly increased both TBARS and hydroperoxide formation when calcium concentrations were 2-fold greater than EDTA concentrations. These results indicate that heat-processed salmon oil-in-water emulsions with high physical and oxidative stability could be produced in the presence of EDTA.

Voltammetric study of the influence of EDTA on the silver electrodeposition and morphological and structural characterization of silver films

The electrodeposition of silver onto platinum from an alkaline electrolyte containing EDTA (ethylenediaminetetraacetic acid) was investigated. Voltammetric studies indicated that the reduction process is influenced thermodynamically and kinetically by the EDTA concentration. Moreover, hydrodynamic studies showed that silver deposition involved different silver complexes, depending on the EDTA concentration. Scanning electron microscopy analysis showed that the presence of EDTA in the plating bath was beneficial, since the silver films coated the substrate completely, regardless of the EDTA concentration. Furthermore, the silver films were uniform, without cracks and with fine granularity, while in the absence of EDTA the granularity was rough. Energy dispersive X-ray spectroscopy showed that carbon was not incorporated into the silver films. X-ray diffraction analysis of the Ag deposits obtained at various EDTA concentrations indicated the occurrence of polycrystalline silver and that the main orientation was (1 1 1), as found in the silver film obtained from a cyanide bath.

Mechanisms Underlying the Endothelium-Independent Relaxation Induced by Angiotensin II in Rat Aorta

It has been suggested that low concentrations of angiotensin II cause vasoconstriction, whereas high concentrations evoke vasodilation. Thus, this work aimed to characterize functionally the mechanisms underlying angiotensin II-induced relaxation, at high concentration, in isolated rat aortic rings. Vascular reactivity experiments, using standard muscle bath procedures, showed that angiotensin II (1-30 microM) concentration-dependently induces relaxation of phenylephrine-precontracted rings with intact or denuded endothelium. The relaxation was not altered in the presence of ethylenediamine tetraacetic acid (EDTA), a nonselective inhibitor of metalloprotease. The selective antagonist of AT2 receptors, PD123319, inhibited angiotensin II-induced relaxation. Conversely, losartan or A-779, selective AT1 and Ang1-7 receptor antagonists, respectively, did not alter the relaxation induced by angiotensin II. HOE-140, a selective antagonist of the bradykinin B2 receptor, and amiloride, a Na+/H+ exchanger inhibitor, abolished angiotensin II-induced relaxation. Administration of exogenous bradykinin on precontracted tissues produced concentration-dependent relaxation, which was also inhibited by HOE-140. Preincubation of denuded-rings with NG-nitro-L-arginine methyl ester (L-NAME), 1H-[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one (ODQ), indomethacin, or tetraethylammonium (TEA) reduced angiotensin II-induced relaxation. The combination of L-NAME, indomethacin, and TEA completely abolished the relaxation induced by angiotensin II. 4-Aminopyridine (4-AP) as well as charybdotoxin reduced angiotensin II-induced relaxation. On the other hand, neither apamin nor glibenclamide altered the relaxation induced by angiotensin II. The major new finding of this work is that it demonstrated functionally the existence of AT2 receptors located on smooth muscle of rat aortic rings that mediated vasorelaxation via stimulation of B2 receptors by bradykinin, which in turns results in the activation of the NO-cGMP pathway, vasodilator cyclooxygenase product(s), and voltage-dependent and Ca+-activated large-conductance K+ channels.

Hyphenation of flow injection on-line preconcentration and ICP-MS for the rapid determination of 226Ra in natural waters

A novel, sensitive, and rapid method is developed for the preconcentration/separation of 226Ra in natural waters using a flow injection (FI) design based on a sequential on-line ion exchange preconcentration coupled with ICP-MS. 226Ra is extracted using an Ln resin (HDEHP) from the sample at pH 10.6 in the presence of ethylenediamine tetraacetic acid (EDTA) diammonium salt, whereas Ca and Mg, which form stable complexes with EDTA, are not retained on the column. Quantitative elution of 226Ra from the Ln resin is achieved using 5 M HNO3. The separation of Ra from Ba and Sr is subsequently performed by the selective retention of Sr and Ba on an Sr*Spec resin, placed between the Ln resin and the Apex-Q system. In addition to being accurate and rapid for 226Ra determination, this method is effective in eliminating spectral (88Sr138Ba) and non-spectral (Ca, Mg) interferences. Using a 20 mL sample, a detection limit (3σ) of 457 fg L−1 (16.92 mBq L−1) was obtained with a sample throughput of 3.5 samples h−1. The precision for 6 replicate measurements of 5 pg L−1 (185.18 mBq L−1) 226Ra was better than 4%. The method was applied to the analysis of natural waters, where the concentration of 226Ra was found to be in the range 1.2 to 2.4 pg L−1 (44.4 to 88.8 mBq L−1), lower than the maximum acceptable concentration (MAC) for 226Ra of 16.2 pg L−1 (600 mBq L−1), recommended in the Guideline for Canadian Drinking Water Quality.

241Am, 137Cs, Sr and Pb uptake by tobacco as influenced by application of Fe chelators to soil

To determine the potential for phytoextraction of 241Am and other contaminants from soil, accumulation of 241Am, 137Cs, Sr, Fe, Al, Pb, and Mg by tobacco was determined for soil applications of two concentrations of ethylenediaminetetraacetic acid (EDTA), citric acid, and ascorbic acid. In tobacco receiving EDTA at 3.1 mmol/kg of soil, 241Am content of plants averaged 15 Bq/kg (ranging up to 26 Bq/kg) while Fe concentrations became constant at 4.5 mmol/kg. Soil treatment with 18.8 mmol/kg EDTA resulted in average 241Am concentrations of 29 Bq/kg (19 times higher than controls). Uptake of Pb was similar to 241Am. In these samples, Fe increased to a maximum of almost 18 mmol/kg and 241Am content increased linearly with both Fe and Al. Plants receiving ascorbic and citric acids took up smaller quantities of 241Am, Pb, and Fe, even though these reagents were able to elute about as much Fe from the soil as EDTA. Synchrotron microbeam X-ray fluorescence (SXRF) was used to determine radial distributions of elements in roots and stems with and without EDTA treatment. SXRF maps indicate differences in behavior between Fe and Pb that are consistent with the bulk plant observations and provide insight into changes in metal content of the roots in the presence of EDTA.

Electron transfer reaction in the chromium(VI)-manganese(II) system in the presence of ethylenediaminetetraacetic acid (EDTA)

Upon addition of Cr VI to a solution of ethylenediaminetetraacetic acid (EDTA) and Mn II, a transient species appears which has an absorption maximum at 500 nm. Kinetic studies of the outer-sphere oxidation of the Mn II-EDTA complex with the Cr VI-EDTA complex have been investigated by visible spectrophotometry at 25 °C. The formation of a transient species has been characterized spectrophotometrically and the encounter complex formation constants have been determined (KOS = 1.75 × 102 and 1.66 × 103 mol-2 dm6 for [EDTA] and [MnII] variations, respectively). The effect of total [EDTA], [MnII], [Cr VI] and [HClO4] on the rate of the reaction was determined. On addition of HClO4, there is a decrease in the rate constants. The reaction product is the CrIII-EDTA complex with λmax = 400 and 550 nm. On the basis of the various observations and product characterization a most plausible outer-sphere mechanism has been envisaged.

Synthesis, Characterization, and Biological Application of Size-Controlled Nanocrystalline NaYF4:Yb,Er Infrared-to-Visible Up-Conversion Phosphors

Nanocrystalline infrared-to-visible up-conversion phosphors, ytterbium and erbium co-doped sodium yttrium fluoride, were synthesized. Spherical particles with narrow size distribution were prepared by a co-precipitation method in the presence of ethylenediaminetetraacetic acid (EDTA). Particles of controlled size in the range of 37 to 166 nm diameter were obtained by adjusting the molar ratio of EDTA to total lanthanides. Although the as-prepared nanoparticles emit very weak up-conversion fluorescence when excited by infrared light, the emission was enhanced by up to 40-fold after they were annealed at temperatures between 400 and 600 degreesC. By comparison with the bulk phosphor, the luminescence efficiency of the nanoparticle was estimated to be 1%. Factors affecting the particle size and their up-conversion fluorescence intensity were investigated by various microscopic and spectroscopic techniques. Preliminary results demonstrated the nanoparticles as promising up-converting fluorescence labels in the detection of biological interactions.

Iron-Humate as a Source of Iron for Plants

An investigation in three replications was conducted to study the release and diffusion of iron (Fe) from iron-humate (Fe-HA) chelates and to assess its availability to growing plants. Labeled, 59Fe-HA, chelates, contained in dialysis bags, were dialyzed against distilled water, a Hoagland nutrient solution, a solution of 10−4 ethylenediamine tetraacetic acid (EDTA) or diethylenetriamine pentaacetic acid (DTPA), and 10−4 M citric acid, and the amount of radiation in the respective solutions measured at 1, 4, and 14 days after dialysis. Assessment of plant uptake of chelated 59Fe-HA and transport of Fe from root to leaf-tissue were examined by growing plant seedlings in Hoagland solutions for 30 days. The Fe source was labeled 59Fe-HA chelates, contained in dialysis bags, placed in the nutrient solutions, treated with or without EDTA. Since different plants were believed to exhibit different mechanisms, called strategies, in absorption and transport of Fe, two types of plants were grown, sunflower and barley plants, representing plants with strategy I and II, respectively. At the end of the growing period, roots, and leaves were sampled, dried, and ground for radiation analysis by the solid scintillation method. The results of diffusion analyses with 59Fe indicated that no diffusion of Fe has occurred from the dialysis bags into the distilled water or Hoagland solutions. Only in the presence of EDTA and DTPA was chelated Fe released by ligand exchange and transported as Fe-EDTA or Fe-DTPA into the outside solutions. Although the results of plant experiments indicate that both types of plants used are capable in absorbing Fe from the HA-Fe source, sunflower (strategy I) roots were apparently more efficient in the transport of Fe from the source to the roots than barley plants (strategy II). However, barley plants, conforming to the strategy II concept, seemed to promote Fe transport from root to leaf-tissue better than sunflower roots.

MgATP-induced conformational change of the catalytic subunit of cAMP-dependent protein kinase

Conformational changes of the cAMP-dependent protein kinase (PKA) catalytic (C) subunit are critical for the catalysis of γ-phosphate transfer from adenosine 5′-triphosphate (ATP) to target proteins. Time-resolved fluorescence anisotropy (TRFA) was used to investigate the respective roles of Mg 2+, ATP, MgATP, and the inhibitor peptide (IP20) in the conformational changes of a 5,6-carboxyfluorescein succinimidyl ester (CF) labeled C subunit ( CFC). TRFA decays were fit to a biexponential equation incorporating the fast and slow rotational correlation times ϕ F and ϕ S. The CFC apoenzyme exhibited the rotational correlation times ϕ F=1.8±0.3 ns and ϕ S=20.1±0.6 ns which were reduced to ϕ F=1.1±0.2 ns and ϕ S=13.3±0.9 ns in the presence of MgATP. The reduction in rotational correlation times indicated that the CFC subunit adopted a more compact shape upon formation of a CFC·MgATP binary complex. Neither Mg 2+ (1–3 mM) nor ATP (0.4 mM) alone induced changes in the CFC subunit conformation equivalent to those induced by MgATP. The effect of MgATP was removed in the presence of ethylenediaminetetraacetic acid (EDTA). The addition of IP20 and MgATP to form the CFC·MgATP·IP20 ternary complex produced rotational correlation times similar to those of the CFC·MgATP binary complex. However, IP20 alone did not elicit an equivalent reduction in rotational correlation times. The results indicate that binding of MgATP to the C subunit may induce conformation changes in the C subunit necessary for the proper stereochemical alignment of substrates in the subsequent phosphorylation.

Synergistic modulation of cystinyl aminopeptidase by divalent cation chelators

Membranes of Chinese hamster ovary (CHO-K1) cells were used to study the opposite modulation of enzyme activity and [ 125 I ]Ang IV binding to cystinyl aminopeptidase (EC 3.4.11.3) by divalent cation chelators. Whereas ethylene diamine tetraacetic acid (EDTA) or ethylene glycol-bis(2-aminoethylether)- N, N, N′, N′-tetraacetic acid (EGTA) alone only slightly affected the enzyme activity, 1,10-phenanthrolin (1,10-PHE) produced a complete and concentration-dependent inhibition. Interestingly EDTA (≥0.05 mM) or EGTA (≥0.15 mM) enhanced the inhibitory effect of 1,10-PHE. Two-site analysis of the corresponding inhibition curves revealed that EDTA and EGTA converted enzymes with low sensitivity towards 1,10-PHE into enzymes with high sensitivity. The combined inhibition by EDTA (0.1 mM) and 1,10-PHE (0.1 mM) could be prevented and reversed by addition of Zn 2+ (at about 0.04–0.1 mM). In contrast, specific binding of [ 125 I ]Ang IV was enhanced in the presence of 1,10-PHE. Binding was only slightly affected by EDTA or EGTA alone. Furthermore, the stimulatory effect of 1,10-PHE was potentiated by EDTA (≥0.05 mM) as well as EGTA (≥0.15 mM). In the presence of EDTA (0.1 mM) and 1,10-PHE (0.1 mM), specific [ 125 I ]Ang IV binding was completely inhibited by Zn 2+ (IC 50 = 39.7 ± 6.2 μM). The present data show that divalent cations such as Zn 2+ are essential for the enzyme activity of cystinyl aminopeptidase and inhibitory for [ 125 I ]Ang IV binding. Modulation of the effects of 1,10-PHE by other chelators such as EDTA or EGTA, suggests that, in addition to the binding site for zinc in the catalytic site, cystinyl aminopeptidase also bears a regulatory divalent cation binding site.

Synthesis and photoluminescence of Pb 9(PO 4) 6 nanocrystals

Rod-like lead phosphate Pb 9(PO 4) 6 nanocrystals were prepared by a surfactant-assisted chemical precipitation method in the presence of ethylenediaminetetraacetic acid and characterized by X-ray diffraction and transmission electron microscopy. The diameter and length of the nanorods were about 15–25 and 50–100 nm, respectively. Furthermore, the possible mechanism for the surfactant-assisted synthesis of Pb 9(PO 4) 6 nanorods has been tentatively presented. Luminescence properties of the Pb 9(PO 4) 6 nanorods were also investigated by photoluminescence spectroscopy.

Precipitation of calcium carbonate in the presence of citrate and EDTA

The influence of process conditions such as feed rate, calcium/carbonate ratio, pH, complexing agents [ethylenediaminetetraacetic acid (EDTA), citrate (CIT)] and their concentration on the average particle size and shape of precipitated calcium carbonate was studied. The precipitation was performed in a semi-batch operated agitated vessel at constant pH by adding sodium hydrogen carbonate to a solution containing calcium chloride. In the absence of a complexing agent, agglomerates of needle-shaped crystals, probably aragonite, are obtained. Increasing feed time and the calcium/carbonate ratio increases the average particle size, whereas the opposite effect is observed for increasing pH. The observations can be related to the level of supersaturation. In the presence of complexing agents and at a concentration ratio of calcium vs. a complexing agent of 6, differently shaped and smaller particles were obtained. Furthermore, the effect of the other parameters on particle size becomes much weaker in the presence of complexing agents. In the presence of EDTA mostly spherical particles were obtained, and in the presence of citrate mainly rhombic particles corresponding to calcite were obtained. The effect on particle shape and size is attributed to interactions of the complexing agents with the faces of the crystalline calcium carbonate.

Accumulation, assimilation and growth inhibition of copper on freshwater alga ( Scenedesmus subspicatus 86.81 SAG) in the presence of EDTA and fulvic acid

Accumulation and growth inhibition of Cu to fresh water alga ( Scenedesmus subspicatus 86.81 SAG) and the influences of ethylenediaminetetraacetic acid (EDTA) and fulvic acid (FA) were examined. These results demonstrated that both EDTA and FA could reduce toxicity of Cu to alga by the way of preventing Cu from being adsorbed by cell wall of alga. When dissolved Cu (Cu dissolved), extracellular Cu (Cu extracellular), and intracellular Cu (Cu intracellular) were differentiated, our results showed that the concentration level of extracellular Cu ([Cu extracellular]) was a good indicator for measuring the toxic effects of Cu on alga growth in complex matrix. Either in the absence or in the presence of EDTA and FA, the concentration of intracellular Cu increased to 0.6–1.5×10 −8 μM per cell when the growth inhibition reached to about 50%. We found that the acute toxicity of copper on unicellular alga could be interpreted by its accumulation at a discrete site or biotic ligand at alga cell wall and critical accumulation of Cu associated with EC 50 was determined to be 1×10 −8 μM per cell. Therefore, the Biotic Ligand Model (BML) could be extended to predict the influence of copper on growth inhibition of alga.

Engineering of dendrimer surfaces to enhance transepithelial transport and reduce cytotoxicity.

To evaluate the cytotoxicity, permeation, and transport mechanisms of PAMAM dendrimers and surface-modified cationic PAMAM dendrimers using monolayers of the human colon adenocarcinoma cell line, Caco-2. Cytotoxicity was determined using the MTT assay. The effect of dendrimers on monolayer integrity was determined from measurements of transepithelial electrical resistance (TEER) and [14C]mannitol apparent permeability coefficient (Papp). The Papp of dendrimers through monolayers was measured in both the apical (A)-to-basolateral (B) and B --> A directions at 4 degrees C and 37 degrees C and also in the presence and absence of ethylenediamine tetraacetic acid (EDTA) and colchicine. The cytotoxicity and permeation of dendrimers increased with both concentration and generation. The cytotoxicity of cationic dendrimers (G2, G3, G4) was greater than that of anionic dendrimers (G2.5, G3.5) but was reduced by conjugation with lauroyl chloride: the least cytotoxic conjugates were those with six attached lauroyl chains. At 37 degrees C the Papp of cationic dendrimers was higher than that of anionic dendrimers and, in general, increased with the number of attached lipid chains. Cationic dendrimers decreased TEER and significantly increased the Papp of mannitol. Modified dendrimers also reduced TEER and caused a more marked increase in the Papp of mannitol. The Papp values of dendrimers and modified dendrimers were higher in the presence of EDTA, lower in the presence of colchicine, and lower at 4 degrees C than at 37 degrees C. The properties of dendrimers may be significantly modified by surface engineering. Conjugation of cationic PAMAM dendrimers with lauroyl chloride decreased their cytotoxicity and increased their permeation through Caco-2 cell monolayers. Both PAMAM dendrimers and lauroyl-PAMAM dendrimer conjugates can cross epithelial monolayers by paracellular and transcellular pathways.

Structural studies of EDTA-induced fibrillation of salmon calcitonin.

The purpose of this work was to determine the structure of an insoluble precipitate formed when mixing approximately equimolar amounts of ethylenediamine tetraacetic acid (EDTA) and salmon calcitonin (sCT). The interaction between EDTA and sCT was examined by measuring solution turbidity kinetics as a function of pH, ionic strength, and addition of ferric ions. Fourier-transformation infrared spectroscopy (FT-IR) identified changes in peptide secondary structure in presence of EDTA. Scanning and transmission electron spectroscopy revealed the macromolecular structure of the sCT/EDTA precipitate. Aggregation of sCT in a time frame up to 1200 min cannot be induced by either pH (range 3.0-7.0) or ionic strength (up to 200 mM) alone, but is a noncovalent interaction between sCT and EDTA. In the pH range 5.0-7.0, a molar binding stoichiometry of sCT/EDTA in the precipitate of 1-3 was determined. We suggest coulombic binding of the free acidic groups of the EDTA to the side chains of the basic amino acids present in the sCT primary sequence. This results in bridging aggregation of the sCT molecules and their precipitation in aqueous solution. The aggregation reaction was blocked by the addition of ferric ions, which bind preferentially to the acidic groups of the EDTA. The sCT/EDTA precipitate redissolves in water in a pH-dependent manner. FT-IR measurements showed a progressive loss of the random coil structure of sCT in water in the presence of EDTA and a simultaneous strong increase in beta-structure. Scanning electron microscopy revealed a fine, sponge-like morphology of the isolated, solid sCT/EDTA precipitate. Transmission electron microscopy delivered final proof of the existence of extensive fibrillation in the sCT/EDTA mixture. EDTA induces rapid fibrillation of sCT in water and the partially reversible formation of a noncovalent, insoluble sCT/EDTA precipitate.

Measuring the bioavailable/toxic concentration of copper in natural water by using anodic stripping voltammetry and Vibrio-qinghaiensis sp.Nov.-Q67 bioassay

Bioassays were carried out in the culture media for Vibrio-qinghaiensis sp.Nov.-Q67 and the influences of alkalinity and different concentrations of chloride, ethylene diamine tetraacetic acid (EDTA) and natural derived fulvic acid (FA) on the labile concentration and toxicity of Cu were investigated. The labile concentration of Cu was obtained by differential pulse anodic stripping voltammetry with a double acidification method (DAM-DPASV). Changes in water alkalinity and chloride concentrations did not affect the labile concentration of Cu, but increases of alkalinity and concentrations of chloride reduced the toxicity on Q67. In the presence of EDTA and FA, both labile concentration of Cu and toxicity were reduced. By excluding Cu-carbonate complexes and Cu-chloride from labile concentration, a bioavailable concentration of Cu (or [Cu*]) was obtained and used to predict the acute toxicity of Cu on Q67. For natural waters, the labile concentration of Cu was measured by DAM-DPASV and [Cu*] was calculated by a MINTEQ A2 software based on composition of waters. This procedure was tested for Guanting Reservoir waters by spiking different concentration Cu. The results showed that [Cu*] was a good indicator for Cu toxicity and could be used in field conditions.

The effect of complexing agents on the DMF–chromium(VI) reaction. A kinetic study

The kinetics of the reduction of chromium(VI) by dimethylformamide (DMF) in the presence of ethylenediaminetetraacetic acid (EDTA) and 2,2′-bipyridyl (bpy) was investigated in aqueous HClO4 acid solutions spectrophotometrically. The experimental findings, that the reaction has an induction period followed by autoacceleration, is explained. After the reduction, chromium(III) is present as the EDTA- and bpy-complexes, although such complexes form very slowly under the same experimental conditions from chromium(III) and the EDTA and bpy, respectively. Increases in the reaction rate with increasing [EDTA] were observed, while added bpy had negligible effect on the reaction rate. The reaction is first-order each in [CrVI] and [H+]. The first-order kinetics with respect to EDTA at low concentrations shift to zero-order at higher concentrations. The reaction is considered to proceed through the formation of a very stable chromium(VI)–DMF–EDTA complex. The suggested mechanism refers only to the induction period of the reaction. The net rate of oxidation of DMF, as measured by the consumption of chromium (VI), is given by: −d[CrVI]/dt = kK1Kb[H+][DMF]T[EDTA][CrVI]T/(1 + K1[EDTA])(1 + Kb[H+])

A mechanistic study of the ethylenediaminetetraacetic acid-, 2,2′-bipyridyl-, and manganese(II)-assisted one-step two- and three-electron oxidation of lactic acid by chromium(VI)

The kinetic results of the oxidation of lactic acid by CrVI in the absence and presence of ethylenediaminetetraacetic acid (EDTA), 2,2′-bipyridyl (bpy), MnII and CeIV are presented. EDTA, bpy and MnII catalyse the reaction, whereas CeIV acts as an inhibitor. Irrespective of the conditions, the order with respect to [lactic acid] was found to lie between one and two, and one in [CrVI]. In the EDTA, bpy and MnII-catalysed paths, CrVI–EDTA, CrVI–bpy and lactic acid–MnII complexes have respectively been suggested as the active oxidant and reductant. The kinetic and cerium(IV) effect studies are consistent with a one-step two-electron transfer mechanism in the absence/presence of EDTA and bpy where a chromate–ester mechanism experiences a redox decomposition (C—H cleavage) in the rate-determining step. On the other hand, the catalytic effect of MnII is described as a one-step three-electron redox decomposition (C—C cleavage) mechanism. Mechanisms in accordance with the experimental data have been proposed for the reactions. Activation parameters have also been evaluated and discussed.